The invention relates to radiocommunications systems ensuring the link between moving stations and one or more fixed stations on frequency jump "channels" and more particularly to the fixed stations of such a system.
In conventional radiocommunications systems, each fixed station has a group of N transmitter-receiver pairs. Each of these pairs is allocated to a communication throughout the duration thereof. The number N of transmitter-receiver pairs in a fixed station is determined as a function of the intensity of the traffic and the maximum permitted loss rate. Thus, for a traffic of 10 erlangs per charged hour, it is conventionally necessary to provide 15 transmitter--receivers to have a 5% loss rate.
In a system where the links are frequency jump links, a frequency jump law can be allocated to each moving station. The laws of the different moving stations in a space-time-frequency continuum are independent, but change values simultaneously. The values of the frequencies in all of the jump laws are chosen within the same group of predetermined frequencies. Transmission takes place during a time period at a given frequency, each such period separated from other periods by dead times, thus facilitating frequency changes. On the reception side, the fixed stations must monitor all the communications liable to be transmitted and consequently all the reception subassemblies are indispensable, i.e. 15 receivers in the above example for a 10 erlang traffic flow with a 5% loss rate.
However, on transmission, the fixed station manages all the communications with the moving stations of the cell. However, transmitters are among the most costly elements of the infrastructure necessary for the fixed station.